The invention relates generally to the “active implantable medical devices” as defined by Directive 90/385/EEC of 20 Jun. 1990 the Council of the European Communities. This definition includes implants that continuously monitor a patient's heart rhythm and deliver to the heart, if necessary, electrical pulses of stimulation, resynchronization and/or defibrillation in case of rhythm disorder detected by the device. It also includes neurological devices, cochlear implants, drug pumps, implantable biological sensors, and other devices.
These devices include a housing generally designated as a generator, electrically and mechanically connected to one or more intracorporeal leads having electrodes intended to come into contact with the tissues (e.g., myocardium, nerve, muscle, etc.) to which it is desired to apply stimulation pulses and / or collect an electrical signal.
The lead is an object implanted through various vessels, including venous, arterial or lymphatic vessels, and its function is to transmit an electrical signal to the target tissue and/or to collect an electrical potential, typically a potential resulting from a cardiac depolarization wave.
The trend in the field of implantable leads is to reduce the size to make them less invasive and easier to handle through the vessels, the size of implantable leads is now typically around 4 to 6 French (1.33 to 2 mm). Beyond these limits, however, a very large increase in the complexity of design and manufacturing, due to the multiple technical constraints to take into account, is met. However, a reduction to less than 2 French (0.66 mm), provides opportunities for medical applications in various fields ranging from cardiology to neurology, in the presence of a venous, arterial network or even lymphatic network as the cerebral venous network or the coronary sinus venous network.
In neurology, electrical stimulation techniques now enable significant advancements in the field of neuromodulation, a technique which is to stimulate target areas of the brain for treatment of Parkinson's disease, epilepsy and other neurological diseases. New target areas may be reachable, through the network of vessels, using small pacing leads hereinafter referred to as “microleads.” Such microleads ideally have a high level of robustness for ensuring long-term biostability. Such a technique would allow for a less invasive approach of these treatments and especially superior efficacy of treatments.
The implantation of these “microleads” and their precise positioning deep in the target area (e.g., coronary arteries deep brain network), however, pose problems due to the requirement of high flexibility.
Guidewires are used with some leads to aide with positioning. Some guidewires have a threaded structure with high stiffness in the proximal part and low stiffness in their distal part. Guidewires can help reach distant targets in the biological networks, such as arterial, venous, lymphatic networks or even, sometimes, crossing valves and tortuosity particularly narrow. However, most guidewire do not present fatigue strength high enough to be compatible with the particularly strict requirements of permanent implants.
Unlike a guidewire, conventional microleads are very flexible and difficult to implant. Torsional stiffness of conventional microleads is not sufficient to enable transmission over the entire length of the lead body (e.g., to its distal end) of a rotational movement imparted by the operating handle (e.g., at the proximal end). In other words, many conventional microleads have a lack of “torquability.” Furthermore, conventional microleads often lack “pushability”, making it difficult to progress a microlead through the biological network.